1. Field of the Invention
This invention relates to improved chromatography packing material. More particularly, this invention relates to such a packing material comprising a generally spherical metal oxide/hydroxide particle comprised of solid crystals of metal oxide/hydroxide, with the crystals extending radially outward from a central core region and having a shape selected from principally acicular to principally lamellar, and having the surface thereof reacted with a phosphorus-containing material to form a layer thereon thereby to provide an improved chromatographic packing material.
2. Description of the Related Art
Chromatographic packing materials made from organic resins suffer from poor physical strength, poor thermal stability, high cost, solvent swelling, and low capacity. Chromatographic packing materials made from metal oxides such as silica exhibit poor chemical stability at high pH. For many applications, in particular for reversed phase chromatography, a chromatographic packing material with high physical integrity, good chemical stability over high and low pH conditions, specific surface functionalities, good thermal stability, and low cost is needed.
Other metal oxides such as alumina have been used as adsorbents because of the good physical integrity and low cost of alumina. The solubility of alumina in pH ranges between 4 and 9 is very low and the material is, therefore, chemically and physically stable in this pH range. However, beyond this pH range, on either the basic or acidic side, alumina becomes soluble in aqueous media and its physical strength and integrity degrades rapidly.
Modifications of metal oxide/hydroxide materials have been proposed. Wieserman et al U.S. patent application Ser. Nos. 946,870 and 023,423 disclose and claim metal oxide/hydroxide surfaces reacted with phosphonic acid or phosphinic acid to form a monomolecular layer thereon to stabilize the metal oxide/hydroxide by modifying the surface of the particle. Wieserman et al U.S. patent application Ser. No. 023,429 (U.S. Pat. No. 4,786,628) discloses and claims a chromatographic packing material comprising a metal oxide/hydroxide particle reacted with phosphonic acid to form a monomolecular layer thereon which provides a chromatographic packing material having good pH stability as well as high efficiency.
Martin et al U.S. patent application Ser. No. 023,312 discloses and claims the formation, on a metal oxide/hydroxide surface such as an aluminum oxide/hydroxide, of a monomolecular layer of a phosphorus-containing organic material having 1-2 phosphorus groups thereon. The phosphorus-containing groups described therein may comprise phosphoric acid monoesters or diesters.
Wilhelmy U.S. patent application Ser. Nos. 940,354 and 022,735 disclose and claim the formation of an aluminum hydroxide particle of extended area which comprises a generally spherical aluminum hydroxide particle comprised of solid crystals of aluminum hydroxide with the crystals extending radially outward from a central core region and having a shape selected from principally acicular to principally lamellar.
Venables et al U.S. Pat. No. 4,308,079 teaches the treatment of an aluminum oxide surface of an aluminum substrate with a monomolecular layer of an amino phosphonate compound such as nitrilotris (methylene) triphosphonic acid to retard hydration of the aluminum oxide to aluminum hydroxide to provide a more stable microporous surface which is particularly suited to commercial adhesives. The presence of the hydrated oxide is said to interfere with the formation of a satisfactory bond between the adhesive and the oxide, while the phosphonate treatment is said to inhibit the conversion of the oxide to hydroxide without interfering with subsequent bonding of the adhesive to the oxide.